Plastic products having highly reflective surfaces are being employed with increasing frequency as mirrors and reflectors in various applications including advertising. Plastic reflectors offer several advantages over conventional mirrored glass articles including improved manufacturing economy and the ease with which plastic reflectors may be formed into any of various three-dimensional shapes.
Previously, three-dimensional, mirrored plastic products were produced by first forming a sheet of suitable thermo-plastic material into a three-dimensional shape. The forming process involved heating the sheet to forming temperature and then using either gravity or a vacuum to draw the sheet over a tool or die corresponding to the final shape of the product. After the formed plastic had cooled, the surfaces of the product were metallized with a reflective metal coating; this was usually accomplished using conventional vacuum deposition techniques. This sequence of processing steps is undesirable, however, since special vacuum deposition equipment may be required to accommodate the plastic substrate after it has been formed into a three-dimensional shape. Moreover, it is substantially more difficult to obtain a deposited metal coating which is substantially even in thickness, particularly where the surfaces of the plastic substrate are irregular, i.e., curved, angular, wavy.
Mirrored (metallized) plastic sheets are presently commercially available. However, it has not been heretofore possible to convert these mirrored sheets into three-dimensional shapes because of a phenomena known in the art as "blushing". Blushing describes the appearance of the mirrored finish after forming has been completed, in which the reflectivity of the finish has been substantially reduced and in which the finish appears substantially grey, rather than highly reflective. A blushed finish is one in which the continuous metallic reflective coating is converted to a multiplicity of microfractures which refract, rather than reflect, light impinging on the surface of the article. Blushing is believed to be caused by differences in mechanical properties of the plastic substrate and the metallic coating, along with the tendency of the plastic substrate to give off residual gases, when heated, during the forming process, which adversely react with the molecules of the metallic coating.